The present invention relates to an electrically powered fastener tool, and more particularly to an electrically powered fastener tool with an on-board controller.
Electrically powered fastener tools are well-known in the art for applying torque to fasteners. These tools are commonly used in assembly lines for assembling parts together and are often in used in the assembly of automobiles and aircraft, among other things. The typical fastening system has a hand-held tool with a rotatable fastener engaging member and a motor for rotating the member. The user engages the fastener engaging member with a fastener and activates the motor to apply torque to the fastener. A controller is used to monitor the performance of the tool and perform predetermined operations. Such operations may include signaling the user whether the fastening job has been completed or remains uncompleted; or decelerating the speed of the motor as a target torque is approached to prevent torque overshoot.
In conventional systems, this controller has been housed in a stationary unit separate from the tool and is electrically connected to the motor through a set of wires. One reason for housing the controller separate from the tool itself is the electromagnetic noise generated by the tool""s motor. Specifically, during operation, the motor generates electromagnetic noise in the form of a flux field as it converts electricity to torque, and this noise may induce currents in the circuitry of the controller or its associated components (particularly where analog signals are used), thereby interfering with the controller""s operations and thus overall tool performance. Also, because the motor housing in the tool is electrically coupled to earth ground (for safety purposes in the event a live wire becomes loose and contacts the motor housing), the stationary unit houses large chokes and/or filters for reducing or eliminating noise generated in the earth ground line, which is undesirable and on which there are legal limitations. Specifically, because the motor housing is separated from the motor stator by insulating material, a capacitive coupling effect can create a charge in the motor housing, which in turn is transmitted along the earth ground line as noise. The large filters and/or chokes filter out this noise. Thus, the purpose of the conventional approach of using a stationary unit is two-fold with respect to noise problems created by the motorxe2x80x94(1) to separate the controller from motor noise, and (2) to house the large chokes and/or filters used for reducing or eliminating noise on the earth ground line.
U.S. Pat. No. 5,903,462, the entirety of which is hereby incorporated into the present application for all purposes, discloses a hand-held type fastener tool in which the controller is carried on-board within the housing. However, the ""462 patent does not disclose a suitable arrangement for dealing with line emissions in the earth ground line to which the motor housing should be electrically coupled; nor does it provide a solution for minimizing the possibility of inducing currents in the controller circuitry by the motor""s flux field. Specifically, the ""462 patent does not provide a solution for avoiding the need for large filters and/or chokes on-board in the controller, or in a separate unit along the power cord. Mounting a large filter and/or choke suitable for dealing with such noise to the tool itself is not a practical option, as they are relatively bulky and would add undesirable weight and/or size to a hand-held tool. Although tool controllers typically use small chokes and/or filters, these are not designed for filtering out the noise that is transmitted along the earth ground line. Mounting a large filter and/or choke separately along the power cord is also undesirable as it still requires the use of a separate component for housing the same, and incurs the additional costs attendant with including it on the cord.
The present invention is directed to providing a design solution that allows a controller to be mounted on-board an electric fastener tool, without the need for using the large filters and/or chokes typically needed for dealing with noise transmitted back along the earth ground line of the power source. Thus, an aspect of the invention provides a hand-held type electrically powered fastener tool for performing a fastening job wherein torque is applied to a fastener using electrical power supplied from an electrical power source having live, neutral, and earth ground lines. The tool comprises a housing constructed and arranged to be manually carried by a user; and an electrically-powered motor. The motor has an electroconductive outer housing adapted to electrically couple to the earth ground line of the electrical power source, a stator received within the outer housing, and a rotor received within the outer housing and rotatable relative to the stator. The motor electrically couples to the live and neutral lines of the electrical power source and converts electrical power from the electrical power source into rotation of the rotor. Preferably, the motor is electrically coupled to the power source indirectly through the controller for allowing the controller to control the motor. A fastener engaging member is carried on the housing. The fastener engaging member is operatively connected to the rotor of the motor for rotation therewith and is engageable with a fastener in torque transmitting relation to enable a fastening job to be performed by engaging the fastener engaging member with the fastener and supplying electrical power to the motor to affect rotation of both the rotor and the fastener engaging member to thereby apply torque to the fastener. An on-board controller is carried on the housing and operable in accordance with a logic scheme. The controller is adapted to monitor the fastening job and perform predetermined operations in accordance with the logic scheme based on the monitoring of the fastening job. Preferably, this includes controlling the motor in accordance with a logic scheme based on feedback from within the tool.
The tool further comprises a shield comprising:
(a) an electroconductive element encircling the stator and adapted to electrically couple to the neutral line of the electrical power source,
(b) a first insulation layer encircling the stator between the stator and the electroconductive element so as to insulate the electroconductive element from the stator, and
(c) a second insulation layer encircling the electroconductive element between the electroconductive element and the electroconductive housing so as to insulate the electroconductive housing from the electroconductive element.
By electrically coupling the motor housing to the earth ground line, the safety of grounding the motor housing is achieved. Moreover, by electrically coupling the electroconductive element to the neutral line of the power source, the motor noise, including any current induced in the electroconductive element and/or charge created in the electroconductive element, is transmitted to the neutral line back to the power source, instead of along the earth ground line via the motor housing. While some minor capacitive coupling may occur (but not necessarily) between the electroconductive element and the motor housing, this amount is relatively small and is not problematic.
Optionally, the electroconductive element is a metallic mesh element, and may be made of copper.
Also optionally, the tool""s controller may further comprise an AC/DC rectifier for electrically coupling the controller to the power source. The AC/DC rectifier would have at least live and neutral terminals for electrically coupling to the live and neutral terminals of the power source, respectively, and the electroconductive element would be electrically coupled to the neutral terminal of the AC/DC rectifier.
Other objects, features, and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims.